Light emitting device

ABSTRACT

A light emitting device includes: a light emitting element having a dominant wavelength in a range greater than or equal to 380 nm and less than or equal to 470 nm; a wavelength conversion member that is disposed on the light emitting element and includes: a translucent member, and a first fluorescent material layer interposed between the light emitting element and the translucent material, the first fluorescent material layer comprising a resin that contains a first fluorescent material, and the first fluorescent material comprising at least one compound selected from (Ca, Sr)AlSiN 3 : Eu and (Ca, Sr, Ba) 2 Si 5 N 8 : Eu; and a covering member that covers sides of the wavelength conversion member and surrounds the light emitting element, the covering member comprising light reflecting material and a second fluorescent material, and the second fluorescent material comprising at least one compound selected from (Ca, Sr)AlSiN 3 : Eu and (Ca, Sr, Ba) 2 Si 5 N 8 : Eu.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/831,191, filed on Mar. 26, 2020, which claims priority under35 U.S.C. § 119 to Japanese Patent Application No. 2019-062816, filed onMar. 28, 2019, the contents of which are incorporated herein byreference in their entireties.

BACKGROUND 1. Field of the Invention

The present disclosure relates to a light emitting device.

2. Description of the Related Art

In recent years, development of the chip-scale package (CSP), which hasessentially the same surface area as a light emitting element (chip),has evolved. Chip-scale packaging allows the number of light emittingdevices and their circuit board mounting locations to be easily modifieddepending on requirements. This increases flexibility in the design ofequipment such as lighting.

For example, Japanese Patent Publication No. 2012-134355 describes alight emitting device that has a light emitting element; a fluorescentmaterial (phosphor) layer disposed on top of the light emitting elementthat changes the wavelength of light emitted by the light emittingelement; a translucent member on which the fluorescent material layer isformed and that is disposed above the fluorescent material layer; andreflecting material disposed adjacent to the lateral surfaces of thelight emitting element, the fluorescent material layer, and thetranslucent member. In this light emitting device, the reflectingmaterial reflects light from the light emitting element and fluorescentmaterial layer to attain high front-view luminance (brightness).

Because the surface area of the package for this light emitting deviceis essentially the same as the light emitting element, a covering memberthat covers the lateral surfaces of the light emitting element isaccordingly thin. As a result, light from the light emitting element canleak through the covering member and can cause observationdirection-dependent color non-uniformity (uneven color), which ischromaticity variation that depends on the direction from which thelight emitting device is observed. For example, in a light emittingdevice that emits red light using a light emitting element that emitsblue light, large color differences can result from light emittingelement light leaking through the covering member and this can causechromaticity to vary perceptibly with the direction of light emission.

One object of certain embodiments of the present invention is to providea light emitting device with improved color uniformity.

SUMMARY

According to one embodiment, a light emitting device includes a lightemitting element having a dominant wavelength in a range greater than orequal to 380 nm and less than or equal to 470 nm, a wavelengthconversion member that is disposed on top of the light emitting elementand includes a first fluorescent material, and a covering member thatcovers the sides of the wavelength conversion member and surrounds thelight emitting element. The light emitting device emits light with aspectrum having a dominant wavelength in a range greater than or equalto 610 nm and less than or equal to 780 nm. The covering member includeslight reflecting material and a second fluorescent material, and thespectrum of the second fluorescent material has a dominant wavelengththat differs from that of the light emitting device by less than orequal to 30 nm. Chromaticity of light emitted by the light emittingdevice is within a four-sided region on a CIE (Commission internationalede l'eclairage) 1931 chromaticity diagram, where chromaticitycoordinates (x, y) are (0.645, 0.335) at a first point, (0.665, 0.335)at a second point, (0.735, 0.265) at a third point, (0.721, 0.259) at afourth point, and a first line joins the first and second points, asecond line joins the second and third points, a third line joins thethird and fourth points, and a fourth line joins the fourth and firstpoints to define the four-sided region of the chromaticity diagram.

According to another embodiment, a light emitting device includes alight emitting element having a dominant wavelength in a range greaterthan or equal to 380 nm and less than or equal to 470 nm, a wavelengthconversion member that is disposed on top of the light emitting elementand includes a first fluorescent material, and a covering member thatcovers the sides of the wavelength conversion member and surrounds thelight emitting element. The light emitting device emits light with aspectrum having a dominant wavelength in a range greater than or equalto 610 nm and less than or equal to 780 nm. The covering member includeslight reflecting material and a second fluorescent material, and thespectrum of the second fluorescent material has a dominant wavelengththat differs from that of the light emitting device by less than orequal to 30 nm. The second fluorescent material included in the coveringmember is at least one compound selected from (Ca, Sr)AlSiN₃: Eu and(Ca, Sr, Ba)₂Si₅N₈: Eu, and the first fluorescent material included inthe wavelength conversion member is at least one compound selected from(Ca, Sr)AlSiN₃: Eu and (Ca, Sr, Ba)₂Si₅N₈: Eu.

According to certain embodiments of the present disclosure, a lightemitting device having improved color uniformity can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

More complete appreciation of the invention and many of its attendantadvantages can be readily obtained as the invention becomes betterunderstood by reference to the subsequent detailed descriptionconsidered in conjunction with the following accompanying drawings.

FIG. 1A is a schematic plan view showing one example of a light emittingdevice for the first embodiment of the present invention; FIG. 1B is across-section through the line IB-IB in FIG. 1A; and FIG. 1C is anenlarged cross-section view of one part of FIG. 1B.

FIG. 2 is a chromaticity diagram showing light emitting devicechromaticity for the fluorescent materials of FIG. 1B and comparativeexample 1.

FIG. 3 is a cross-section of a light emitting device for the secondembodiment of the present invention.

FIG. 4 is a graph showing light emission spectra for the fluorescentmaterials of FIG. 1B.

FIG. 5 is a schematic diagram showing the directions for measuringdirectional (orientation dependent) chromaticity.

FIGS. 6A and 6B are diagrams showing directional chromaticity of a lightemitting device of comparative example 1.

FIGS. 7A and 7B are diagrams showing directional chromaticity of a lightemitting device of comparative example 2.

FIGS. 8A and 8B are diagrams showing directional chromaticity of a lightemitting device of the first embodiment.

FIGS. 9A and 9B are diagrams showing directional chromaticity of a lightemitting device of the second embodiment.

FIGS. 10A and 10B are diagrams showing directional chromaticity of alight emitting device of comparative example 3.

FIGS. 11A and 11B are diagrams showing directional chromaticity of alight emitting device of comparative example 4.

FIGS. 12A and 12B are diagrams showing directional chromaticity of alight emitting device of the third embodiment.

FIGS. 13A and 13B are diagrams showing directional chromaticity of alight emitting device of the fourth embodiment.

DETAILED DESCRIPTION

Embodiments and examples of the present invention are described belowwith reference to the accompanying drawings. Common reference numeralsdesignate corresponding or identical elements throughout the variousdrawings.

However, the embodiments and examples described below are merelyexamples intended to concretely illustrate technical concepts of thepresent invention, and the present invention is not limited to thedescriptions below. Properties such as the size and spatial relation ofcomponents shown in the figures may be exaggerated for the purpose ofclear explanation. Detailed description of parts having the same nameand reference numeral (corresponding or identical elements) isappropriately abbreviated. Further, in the embodiments and examples ofthe present invention, a single component can serve multiple functionsand a plurality of structural elements of the invention can beimplemented with the same component. In contrast, the functions of asingle component can be separated (distributed) and implemented by aplurality of components. Explanations used to describe one embodiment orexample may be used in the description of other embodiments andexamples. In the following descriptions, terms indicating directionaland positional relations (such as “upper,” “lower,” “right,” “left,” andexpressions that include those positional relation terms) are used asrequired. However, use of those terms is merely intended to indicaterelative directions and positions, to make the invention easilyunderstood when referring to the drawings. The technical scope of theinvention is not limited by the meaning of those terms unless explicitlystated. In the present application, the term “is provided” is used witha meaning that includes provision of separate elements, as well asprovision of elements configured as a single unit.

In this application, the relation between color name and chromaticitydiagram coordinates, and the relation between the color name ofmonochromatic light and its range of wavelengths is in accordance withJapanese Industrial Standard (JIS) Z8110. In addition, when a pluralityof substances are present in each component of a compound, unlessotherwise noted, the content (amount) of each component is taken to meanthe total amount of the plurality of substances included in thecompound.

First Embodiment

A light emitting device according to a first embodiment of the presentinvention is shown in FIGS. 1A-1C. FIG. 1A is a plan view of the lightemitting device 100 according to the first embodiment, FIG. 1B is avertical cross-section through the line IB-IB in FIG. 1A, and FIG. 1C isan enlarged cross-section view of an end region of the adhesive layer 4shown in FIG. 1B. The light emitting device 100 shown in these figuresis provided with a mounting substrate 1, a light emitting element 2, awavelength conversion member 30, and a covering member 50. The mountingsubstrate 1 has a substrate primary surface that faces in the samedirection as the light emitting surface of the light emitting device100. The light emitting element 2 is mounted in “flip chip” fashion viaconducting material 6 on the primary surface of the mounting substrate1. The wavelength conversion member 30 is joined to the upper surface(primary surface) of the light emitting element 2 via the adhesive layer4.

A Covering Member 50

The covering member 50 covers the lateral surfaces of the wavelengthconversion member 30 and the light emitting element 2, which is joinedwith the wavelength conversion member 30. The covering member 50contains resin 51. For example, resins such as phenol resin, epoxyresin, bismaleimide triazine resin, polyphthalamide resin, and siliconeresin can be used as the resin 51 in the covering member 50. Thecovering member 50 also contains light reflecting material 52 and secondfluorescent material 53 within the resin 51. Materials such as titanium(di)oxide, alumina, and silicon (di)oxide can be used as lightreflecting material 52. Although the second fluorescent material 53 isalso described later, the dominant wavelength of the spectrum of thesecond fluorescent material 53 differs from the dominant wavelength ofthe spectrum of the light emitting device by 30 nm or less. Further,little change with angular direction (of the incident light) is adesirable characteristic for the second fluorescent material 53.Material that absorbs light emitted by the light emitting element suchas pigments can also be included in the covering member 50.

A Wavelength Conversion Member 30

The upper surface of the wavelength conversion member 30 serves as thelight emitting surface and is exposed from the covering member 50. Thewavelength conversion member 30 is made up of a fluorescent materiallayer 31 that includes first fluorescent material 33, and a translucentmember 32 configured as a single unit on top of the fluorescent materiallayer 31.

The light emitting device 100 can also be provided with a semiconductorelement 7. The semiconductor element 7 is a protection device such as aZener diode that protects the light emitting element 2 when reversevoltage is applied (e.g. plugged-in-backwards). Depending onrequirements, the semiconductor element 7 can be omitted. The followingdescribes each component of the light emitting device 100 in detail.

Mounting Substrate 1

It is desirable for the mounting substrate 1 to have insulatingproperties. In addition, the mounting substrate 1 is preferably materialthat does not easily pass light from the light emitting element 2 orexternal light (i.e. opaque material). For example, ceramics such asalumina and aluminum nitride, or resins such as phenol resin, epoxyresin, polyimide resin, bismaleimide triazine resin, and polyphthalamideresin can be used as mounting substrate material. When resin material isused, inorganic filler such as glass fiber, silicon oxide, titaniumoxide, and or alumina can be mixed into the resin as necessary. This canfacilitate improved mechanical strength (robustness), lower thermalexpansion coefficient, and higher light reflectivity.

Light Emitting Element 2

The light emitting element 2 is preferably a light emitting diode, and alight emitting diode with a wavelength appropriate for the applicationcan be selected. For example, nitride semiconductors(In_(x)Al_(y)Ga_(1-x-y)N, 0≤x, 0≤y, x+y≤1) that can emit shortwavelength light for efficient excitation of the first fluorescentmaterial 33 can be proposed as the light emitting element 2. A varietyof wavelengths can be selected depending on semiconductor layer materialand crystallinity mix. The light emitting element 2 emits light with adominant wavelength within a range between 380 nm and 470 nm.

A Wavelength Conversion Member 30

The wavelength conversion member 30 is configured as a fluorescentmaterial layer 31 of resin containing first fluorescent material 33, anda translucent member 32 such as glass. However, the wavelengthconversion member is not limited to this configuration. For example, thewavelength conversion member 30 may be configured as a fluorescentmaterial ceramic that is a sintered mixture of fluorescent and ceramicmaterials, a fluorescent material sheet that is resin with fluorescentmaterial mixed in and formed in a sheet, and glass that includesfluorescent material.

Fluorescent Material Layer 31

The fluorescent material layer 31 absorbs at least part of the lightemitted by the light emitting element 2 and re-emits light at adifferent wavelength. Translucent material such as resin, glass, orother inorganic materials with first fluorescent material 33 mixed as abinder can be used to form the fluorescent material layer 31. Thefluorescent material layer 31 can be formed as a single layer containingone type of fluorescent material, as a single layer containing a mixtureof two or more types of fluorescent material, or as a laminate of two ormore single layers. In addition, coloring agent, light diffusing agent,and filler can also be added as required.

In the example shown in FIG. 1B, the wavelength conversion member 30 isformed with a surface area larger than the surface area of the lightemitting element 2 upper surface (primary surface). This arrangementintroduces light emitted by the light emitting element 2 into thewavelength conversion member 30 over a wide area and can reduce colornon-uniformity. However, the present invention is not limited to thisconfiguration and the surface area of the wavelength conversion member30 can also be smaller than that of the primary surface of the lightemitting element 2. In that case, the front-side brightness of the lightemitting device can be increased.

The fluorescent material layer 31 is formed on a surface of thetranslucent member 32 (further described below) by a method such asprinting. In the present embodiment, fluorescent material layer 31disposition not only includes direct contact with a surface of thetranslucent member 32, but also includes connection with the translucentmember 32 via other materials such as adhesive. For example, compressionbonding, thermally fused connection, sintering, adhesion by organicadhesive, and adhesion by inorganic adhesive (e.g. low melting pointglass) are possible connection methods. Methods used to form thefluorescent material layer include printing methods, compressionmolding, fluorescent material electro-deposition, and fluorescentmaterial sheet formation. In a printing method, a paste is prepared thatincludes fluorescent material, binder, and solvent, and that paste isapplied to a surface of the translucent member 32 and dried to form thefluorescent material layer. Organic resin binders such as epoxy resin,silicone resin, phenol resin, and polyimide resin, or inorganic binderssuch as glass can be used as the paste binder. In compression molding,fluorescent material layer raw material, which is binder containingfluorescent material, is placed on the surface of the translucent member32 in a mold, and compression molded. In fluorescent materialelectro-deposition, a thin conducting film that can pass light is formedon the surface of the translucent member 32, and fluorescent materialcharged using electrophoresis is deposited on the thin film. Finally, influorescent material sheet formation, fluorescent material is mixed andkneaded into silicone resin, and processed into sheet form. Because thismethod employs fluorescent material in sheet form, the thickness of thatsheet can be made as thin as possible from a heat dissipationstandpoint. Here, fluorescent material sheet with a thickness on theorder of 100 μm or less is compression bonded to the translucent member32 to make a consolidated structure.

A thickness of the fluorescent material layer 31 is greater than orequal to 20 μm and less than or equal to 200 μm, and preferably greaterthan or equal to 30 μm and less than or equal to 150 μm. This is becausea thickness greater than 200 μm shows a tendency for reduced heatdissipation. While a fluorescent material layer made as thin as possibleis desirable from a heat dissipation standpoint, if it is made too thin,the amount of first fluorescent material 33 becomes sparse and this hasthe tendency to reduce the range of color (chromaticity range) emitted.With these considerations, the fluorescent material layer 31 thicknessis established as appropriate.

The light emitting device 100 emits red light (JIS red), which accordingto JIS Z8110, is light with a dominant wavelength from nm to 780 nm. Thelight emitting device 100 emits light in a range that is within afour-sided region on the CIE1931 chromaticity diagram shown in FIG. 2.The four-sided region of the chromaticity diagram is defined by fourpoints and four lines connecting those points, where chromaticitycoordinates (x, y) are (0.645, 0.335) at a first point, (0.665, 0.335)at a second point, (0.735, 0.265) at a third point, (0.721, 0.259) at afourth point, and a first line joins the first and second points, asecond line joins the second and third points, a third line joins thethird and fourth points, and a fourth line joins the fourth and firstpoints.

First Fluorescent Material 33

By using a blue light emitting element 2 together with first fluorescentmaterial 33, which emits red light when excited by blue light from thelight emitting element, the light emitting device 100 can emit redlight. Examples of first fluorescent material 33 that can beadvantageously combined with the light emitting element 2 to emit redlight include fluorescent material given by the chemical formulas (Sr,Ca)AlSiN₃: Eu and (Ca, Sr, Ba)₂Si₅N₈: Eu. Other fluorescent materialthat emit red light include, for example, (Ca, Sr, Ba)S: Eu, K₂(Si, Ti,Ge)F₆: Mn, 3.5MgO.0.5MgF₂.GeO₂:Mn, and (Sr, Ca)LiAl₃N₄: Eu. Here, exceptfor special cases, when a plurality of elements in the fluorescentmaterial formula are separated by a comma (,), at least one of thoseelements is included in the chemical composition and two or more ofthose elements can also be included in combination. Also in the presentapplication, a colon (:) in the fluorescent material formula separateselements of the crystal matrix and their molar ratio, which arepositioned before the colon, from activating elements noted after thecolon. Molar ratio indicates the number of moles (proportions) ofelements in the composition of 1 mole of fluorescent material.

To realize a light emitting device 100 that can emit red light, theconcentration of first fluorescent material 31 in the fluorescentmaterial layer 31 is adjusted to make the emitted light red. Forexample, first fluorescent material 33 concentration is made greaterthan or equal to 100 mass % and less than or equal to 200 mass % withrespect to resin, etc.

If first fluorescent material is sufficiently included to keep thechromaticity of light emitted by the light emitting device within thespecified range, a third fluorescent material that emits light fromyellow-green to orange can be additionally mixed with the firstfluorescent material.

Third fluorescent material includes, for example, (Lu, Y, Gd, Tb)₃(Al,Ga)₅O₁₂: Ce, which is the chemical composition ofyttrium-aluminum-garnet system fluorescent material and is subsequentlyabbreviated as (YAG) in this application.

Other fluorescent material that can be added include, for example,Si_(6-z)Al_(z)O_(z)N_(8-z): Eu (0<z<4.2), Ca₃Sc₂Si₃O₁₂: Ce, CaSc₂O₄: Ce,(La, Y, Gd)₃(Al, Si)₆N₁₁: Ce, (Ca, Sr, Ba)₈MgSi₄O₁₆(F, Cl, Br)₂: Eu,(Ca, Sr, Ba)₃Si₆O₉N₄: Eu, (Ca, Sr, Ba)₃Si₆O₁₂N₂: Eu, (Ba, Sr,Ca)Si₂O₂N₂: Eu, (Ba, Sr, Ca, Mg)₂SiO₄: Eu, (Ba, Sr, Ca)Ga₂S₄: Eu, (Ca,Sr, Ba, Mg)₁₀(PO₄)₆(F, Cl, Br, I, OH)₂: Eu, (Ba, Sr, Ca)₃MgSi₂O₈: Eu,Sr₄Al₁₄O₂₅: Eu, (Si, Al)₆(O, N)₈: Eu.

Translucent Member 32

A translucent member 32 is prepared separately from the fluorescentmaterial layer 31, which contains first fluorescent material 33. Thetranslucent member 32 is the part that supports the fluorescent materiallayer 31 formed on its surface. Translucent plate material such as glassor resin can be used as the translucent member 32. Glass can be selectedfrom materials such as borosilicate glass or quartz glass, and resin canbe selected from materials such as silicone resin or epoxy resin.

A thickness of the translucent member 32 should be sufficient to avoidloss of mechanical strength during processing and furnish amplemechanical strength to the fluorescent material layer 31. If thetranslucent member 32 is too thick, it can obstruct miniaturization ofthe light emitting device or degrade heat dissipation. Accordingly, asuitable thickness is desired. The translucent member 32 can alsoinclude light diffusing agent. As the concentration of fluorescentmaterial in the fluorescent material layer 31 is increased, emittedlight becomes more prone to color non-uniformity, and the presence oflight diffusing agent can alleviate color non-uniformity as well asbrightness non-uniformity. For example, titanium oxide, barium titanate,aluminum oxide, and silicon oxide can be used as light diffusing agent.

The upper surface of the translucent member 32, which becomes the lightemitting surface, is not limited to a smooth planar surface, and canhave minute bumps, indentations or general roughness. This can promotescattering of light output from the light emitting surface and canfurther suppress color and brightness non-uniformity. In addition, thelight emitting surface can be treated with an anti-reflection (AR)coating or a distributed Bragg reflector (DBR) film.

Adhesive Layer 4

An adhesive layer 4 intervenes between the light emitting element 2 andthe fluorescent material layer 31. The adhesive layer 4 bonds thefluorescent material layer 31 to the light emitting element 2. Adhesivethat makes up the adhesive layer 4 is material that can effectivelyguide light output from the light emitting element 2 into thefluorescent material layer 31, and preferably is material that canoptically couple the fluorescent material layer 31 with the lightemitting element 2. Specifically, epoxy resin, silicone resin, phenolresin, and polyimide resin are candidate materials. Of those resins,silicone resin, which is extremely durable, is favored as adhesive forthe adhesive layer 4. The adhesive layer 4 is made as thin as possible.This is because, for example, a thin layer improves heat dissipationproperties and reduces light loss due to transit through the adhesivelayer thereby improving the light output of the light emitting device.

In the case in which silicone resin is used as binder in the fluorescentmaterial layer 31, it is desirable to also use silicone resin asadhesive in the adhesive layer 4. This can reduce refractive indexdifferences between the fluorescent material layer 31 and the adhesivelayer 4 and can increase the input of light from the adhesive layer 4into the fluorescent material layer 31.

Semiconductor Element 7

The semiconductor element 7 is separate from the light emitting element2 and is disposed adjacent to the light emitting element 2 on themounting substrate. The semiconductor element 7 can be a semiconductorchip that is similar to a light emitting element except that is notdesigned for light emission, a transistor to control the light emittingelement, or a protection device as described below. A protection deviceprotects the light emitting element 2 from damage or functionaldegradation due to over-voltage application. Specifically, a Zenerdiode, which conducts when a voltage greater than the specified voltageis applied to the light emitting device, serves as the protectiondevice. The protection device is a semiconductor chip that has a p-typeelectrode and an n-type electrode the same as the light emitting element2. However, the protection device is connected in parallel with thelight emitting element 2 in opposite polarity. Namely, the p-electrodeof the protection device is electrically connected to the n-electrode ofthe light emitting element 2 and the n-electrode of the protectiondevice is electrically connected to the p-electrode of the lightemitting element 2 via conducting material 6. In the same manner as thelight emitting element 2, each electrode terminal of the protectiondevice is aligned on top of a corresponding conducting material bump andjoined via heat, ultra-sonic, and/or compression application.

A Covering Member 50

Insulating material is desirable for use as a covering member 50material. To provide some degree of robustness, materials such asthermosetting resin or thermoplastic resin are used. More specifically,phenol resin, epoxy resin, bismaleimide triazine resin, polyphthalamideresin, and silicone resin are candidate materials. Coloring agent and/orfiller can also be added depending on requirements.

A covering member 50 application can be performed, for example, by adispensing tool that can be moved vertically and horizontally withrespect to the mounting substrate 1 held stationary beneath thedispenser. Namely, resin that includes the previously described lightreflecting material 52 and second fluorescent material 53 is preparedand loaded into the dispensing tool. Subsequently, by dispensing resinwhile moving the tip of dispenser nozzle around the light emittingelement, a covering member 50 is applied around the light emittingelement 2 and the semiconductor element 7. The speed at which thedispensing tool moves is appropriately adjusted depending on factorssuch as the viscosity and temperature of the resin being used. Thequantity of resin dispensed can be adjusted by maintaining conditionssuch as constant pressure during dispensing.

The thinnest region of the covering member, which is coating on alateral surface (not adjacent to the semiconductor element 7) of thelight emitting element, preferably has a minimum thickness greater thanor equal to 100 μm and a maximum thickness less than or equal to 300 μmmeasured perpendicular to the lateral surface of the light emittingelement. If the covering member is too thin, light from the lightemitting element can leak through the covering member and cause colornon-uniformity. If the covering member is made thick, it is difficultfor light to escape but the size of the light emitting device becomesexcessively large.

Light Reflecting Material 52

By distributing particulate light reflecting material 52, which does noteasily absorb light from the light emitting element 2 and has arefractive index significantly different from that of the resin base,within the resin base of the covering member 50, light can beefficiently reflected. Light reflecting material 52 preferably includesat least one of the oxides of, for example, yttrium, zirconium,aluminum, titanium, and/or silicon. The amount of light reflectingmaterial 52 included in the resin is preferably greater than or equal to10 mass % and less than or equal to 100 mass % (with respect to theresin).

Second Fluorescent Material 53

By adding second fluorescent material to the covering member 50, lightthat passes through the light reflecting material without beingreflected can be wavelength-converted by the second fluorescent materialmaking it possible to further reduce light emitting device 100 colornon-uniformity. In the case of a light emitting device 100 that emitsred light, essentially all the light emitted by the light emittingelement is wavelength-converted by fluorescent material, and effectivelyno unconverted light emitting element (non-red) light is output from thewavelength conversion member. The difference between the chromaticity oflight emitting element light that passes through the light reflectingmaterial and the chromaticity of light observed exiting the wavelengthconversion member is reduced (due to wavelength-conversion by the secondfluorescent material). Accordingly, this reduces color non-uniformity asa function of the direction from which the light emitting device 100 isobserved.

It is desirable to use second fluorescent material 53 included in thecovering member 50 that is of the same type as the first fluorescentmaterial 33, which is included in the fluorescent material layer 31 ofthe wavelength conversion member 30. For example, fluorescent materialindicated by the formula (Sr, Ca)AlSiN₃: Eu (in this application,subsequently abbreviated by SCASN) and (Ca, Sr, Ba)₂Si₅N₈: Eu can beused.

The second fluorescent material 53 can be material with the samechemical formula as the first fluorescent material 33 included in thefluorescent material layer 31 or material with a different chemicalformula. Second fluorescent material 53 added to the covering member 50has a spectrum with a dominant wavelength that differs from the dominantwavelength of the spectrum of the light emitting device by less than orequal to 30 nm, preferably less than or equal to 20 nm, and morepreferably less than or equal to 10 nm. The average particle diameter ofthe fluorescent material is preferably greater than or equal to 2 μm andless than or equal to 10 μm. The amount of fluorescent material added ispreferably greater than or equal to 0.5 mass % and less than or equal to10 mass % with respect to the resin.

Conducting Material 6

Bumps can be used as conducting material 6, and gold (Au) or gold-alloycan be used as bump material. Other possible conducting materialsinclude eutectic solder (Au—Sn), Pb—Sn, and lead-free solder. AlthoughFIG. 1B shows an example where bumps are used as the conducting material6, the conducting material 6 is not limited to bumps and, for example,conducting paste can be used as well.

Second Embodiment

Underfill can be used together with the covering member 50. An exampleof this configuration is in the light emitting device 200 of the secondembodiment shown in the schematic cross-section of FIG. 3. In the lightemitting device 200 shown in this figure, the same (numeric) referencelabels are used to indicate components that are the same as in thepreviously described first embodiment and their detailed description isabbreviated.

Underfill 70

Underfill 70 is material intended to protect the light emitting element,semiconductor element, and conducting material disposed on the mountingsubstrate from contaminants and detrimental conditions such as dust,moisture, and externally applied force. Depending on requirements,underfill 70 can be established within gaps beneath and between thelight emitting element 2, semiconductor element 7, and conductingmaterial 6.

Underfill 70 material can be, for example, silicone resin or epoxyresin. Additives such as coloring agent, light diffusing agent, filler,and fluorescent material can also be included in the resin material. Bydisposing underfill 70 between the light emitting element 2 and thecovering member 50, light escaping from the bottom side of the lightemitting element 2 is reflected back towards the light emitting element2 and a wavelength conversion member 30, and this can increase lightextraction efficiency from the upper surface of the light emittingdevice. Further, because inclusion of additives such as coloring agent,light diffusing agent, filler, and fluorescent material in the underfillincreases the effect of suppressing light that would otherwise passthrough the covering member 50 (before reaching the covering member 50),light emitting device chromaticity variation with observation directioncan be constrained.

EXAMPLES

While examples of the present invention are described in detail below,the present invention is not limited to these examples.

Fluorescent materials used in the examples and comparative examples areshown in Table 1. Fluorescent materials in Table 1 are SCASN [(Sr,Ca)AlSiN₃: Eu] material: SCASN-1, SCASN-2, and SCASN-3, which havedifferent spectral dominant wavelengths and chromaticity; and YAG[Y3A15012: Ce] material, which has a different chemical formula as wellas different spectral dominant wavelength and chromaticity. The emissionspectrum of each fluorescent material is shown in FIG. 4. For theaverage particle diameter of each fluorescent material, a FisherSub-Sieve Sizer was used to measure Fisher Number according to the “airpermeability principle.” Specifically, a 1 cm³ sample was measured andpacked in the cylindrical test chamber; dry air flow was supplied withconstant pressure to the test chamber; specific surface area wasdetermined from the pressure differential across the test chamber, andthat value was converted to average particle diameter. Fluorescentmaterial chromaticity (coordinates) on a chromaticity diagram are asshown in FIG. 2. In Table 1, fluorescent material “peak wavelength” isthe wavelength at the maximum (peak) relative emission intensity of thefluorescent material emission spectrum (e.g. as shown in FIG. 4).Further, “dominant wavelength” for fluorescent material and lightemitting device spectra is the chromaticity diagram wavelength at theintersection of the extension of a line from the chromaticity diagramwhite point (0.333, 0.333) through the chromaticity coordinates of thefluorescent material with the chromaticity diagram spectral locus ofmonochromatic light (horse-shoe shaped outline of the chromaticitydiagram).

TABLE 1 Dom- Peak inant Average Fluo- Wave- Wave- Particle rescentlength length Chromaticity Diameter Material (nm) (nm) x Y ChemicalFormula (μm) SCASN-1 626 605 0.651 0.349 (Sr, Ca)AlSiN₃: Eu 14.4 SCASN-1633 608 0.658 0.342 (Sr, Ca)AlSiN₃: Eu 11.8 SCASN-1 628 601 0.636 0.363(Sr, Ca)AlSiN₃: Eu 2.4 YAG 566 575 0.470 0.517 Y₃Al₅O₁₂: Ce 3.4

Comparative Example 1

Light emitting devices 100 as shown in FIGS. 1A-1C were made asdescribed below for the examples and comparative examples. A lightemitting element 2 and semiconductor element 7 were positioned on amounting substrate. Specifically, a 1.0 mm by 1.0 mm approximatelysquare light emitting element 2 having a thickness of approximately 0.11mm and a dominant wavelength of 450 nm was fabricated by forming asemiconductor stack on a sapphire substrate. The light emitting element2 was disposed in line with the semiconductor element 7 and mounted viaAu (gold) conducting material 6 in flip-chip fashion to make thesapphire substrate side of the light emitting element the light emittingsurface. The semiconductor element 7 with pre-formed Au bumps wasmounted in flip-chip fashion on patterned conducting runs.

Next, one side (primary surface) of the translucent member 32 was coatedwith a fluorescent material layer 31 by printing. Borosilicate glass insheet-form was used as the translucent member 32. The translucent memberwas formed in a 1.15 mm by 1.15 mm approximately square planar shape,which was larger than the surface of the light emitting element by 0.15mm on each side, and a thickness of the translucent member wasapproximately 0.10 mm. A translucent member 32 in sheet-form had thefluorescent material layer 31, which used SCASN-1 and SCASN-2fluorescent material with silicone resin as binder, printed on oneprimary surface and cut to the appropriate size.

The concentration of fluorescent material (summation of both SCASN-1 andSCASN-2) in the fluorescent material layer 31 was 186 mass %, and theplanar shape of the fluorescent material layer facing the upper surfaceof the light emitting element was the same as that of the translucentmember (a 1.15 mm by 1.15 mm approximately square shape), and athickness of the fluorescent material layer was 80 μm. Because thetranslucent member 32 had a thickness of approximately 100 μm, acombined thickness of the translucent member 32 and fluorescent materiallayer 31 was approximately 180 μm.

Next, silicone resin was disposed as adhesive on the upper surface ofthe light emitting element 2, and the fluorescent material layer 31formed on the surface of the translucent member 32 was joined to thesapphire substrate upper surface of the light emitting element 2. Thesurface area of the fluorescent material layer 31 was larger than thatof the upper surface of the light emitting element 2, and thefluorescent material layer was joined in a manner establishing exposedregions around the light emitting element.

Next, regions around the light emitting element 2, fluorescent materiallayer 31, translucent member 32, and semiconductor element 7 were filledwith a covering member 50. A covering member 50 was disposed along thelateral surfaces of the light emitting element 2, fluorescent materiallayer 31, and translucent member 32, and a covering member 50 wasapplied to completely embed the semiconductor element 7. In comparativeexample 1, dimethyl silicone resin was used as resin 51 in the coveringmember 50, and titanium oxide particles with an average particlediameter of 0.28 μm (measured in the same manner as fluorescent materialaverage particle diameter) were used as light reflecting material 52.Titanium oxide particles were included in the resin with a concentrationof 60 mass %. In comparative example 1, no fluorescent material wasadded to the covering member 50. A covering member thickness was 225 μmin comparative example 1. The covering member thickness is the thicknessmeasured perpendicular to the lateral surface of the light emittingelement from the lateral surface to the outer surface of the lightemitting device 100, and is the thinnest part of the covering member.The covering member thickness is the same on all sides of the lightemitting element except the side adjacent to the semiconductor element.Light emitting devices 100, as shown in FIGS. 1A-1C, were made accordingto this processing sequence.

Comparative Example 2

Light emitting devices of comparative example 2 were made the same wayas those of comparative example 1 except that a smaller 0.8 mm by 0.8 mmapproximately square light emitting element 2 with a thickness ofapproximately 0.11 mm was used.

First and Second Examples

Light emitting devices of the first and second examples were made thesame way as those of comparative example 1 except that SCASN-3 secondfluorescent material 53 was included (with different amounts for eachexample) in the covering member 50.

Comparative Example 3

Light emitting devices of comparative example 3 were made the same wayas those of comparative example 1 except that YAG second fluorescentmaterial 53 was included in the covering member 50.

Comparative Example 4

Light emitting devices of comparative example 4 were made the same wayas those of comparative example 1 except that the amount of titaniumoxide light reflecting material 52 added to the covering member 50 wasreduced to 30 mass % (with respect to the resin 51).

Third and Fourth Examples

Light emitting devices of the third and fourth examples were made thesame way as those of comparative example 4 except that SCASN-3 secondfluorescent material 53 was included (with different amounts for eachexample) in the covering member 50.

Table 2 and Table 4 show, for comparative examples 1-4 and first throughfourth examples, light emitting element size, first fluorescent materialused in the wavelength conversion member, amount of titanium oxide lightreflecting material added to the covering member, second fluorescentmaterial type and amount added to the covering member, and thickness ofthe thinnest part of the covering member measured from the lateralsurface of the light emitting element chip to the outside of the lightemitting device.

The following parameters were evaluated for comparative examples 1-4 andthe first through fourth examples.

Chromaticity and Dominant Wavelength

An optical measurement system combining a multi-channel spectrometer andintegrating-sphere photometer was used to measure chromaticity anddominant wavelength for each comparative example and example. Evaluationresults are shown in Table 3 and Table 5. In addition, chromaticity ofcomparative example 1 is shown on the chromaticity diagram in FIG. 2.

Dominant Wavelength Difference

The difference between the dominant wavelength of the light emittingdevice emission spectrum (i.e. the dominant wavelength of the spectrumof a light emitting device with no second fluorescent material includedin the covering member) and the dominant wavelength of the emissionspectrum of the second fluorescent material included in the coveringmember was computed as dominant wavelength difference in nanometers.Results are shown in Table 3 and Table 5.

Luminous Flux Ratio

A total luminous flux measurement device incorporating anintegrating-sphere photometer was used to measure total luminous fluxfor the light emitting device of each comparative example and example.Luminous flux of comparative example 1 was assumed to be 100% andluminous flux for other comparative examples and examples were computedas a ratio with respect to comparative example 1. Luminous flux ratioresults are also shown in Table 3 and Table 5.

Directional Chromaticity

The relation of measurement direction to chromaticity (angular dependentchromaticity) was investigated for each light emitting device. Fordirectional chromaticity (measurement direction-dependent chromaticity)measurement, the light emitting device for each comparative example andexample was illuminated by passing 350 mA of current, while changing themeasurement direction by rotating the light emitting device with agoniometer, emission chromaticity was measured using a spectraldistribution measurement device (spectral distribution spectrometer)under CIE condition B recommended for “average LED luminance”measurement. The direction of measurement was set by an angle θ measuredfrom the light emitting device optical axis C (that passes through thecenter-point of the light emitting device upper surface parallel to thez-axis). Measurement direction for directional chromaticity(direction-dependent chromaticity) is illustrated by the schematicdiagram in FIG. 5. As shown in this figure, directional chromaticity wasmeasured by varying the measurement angle θ in the x-z plane (xz-planemeasurement) and in the y-z plane (yz-plane measurement). To evaluatethe emitted color, x-coordinate and y-coordinate values in the CIEstandard color system (chromaticity diagram color space) were used(note: color coordinates x and y are not related to the x and y axes inFIG. 5). Light emitting device directional chromaticity was evaluatedusing the θ=0° point as a reference, and color coordinate differences(Δx, Δy) were computed with respect to the reference at each measurementpoint.

Directional chromaticity measurement results for each sample are shownin FIGS. 6A-13B. Because the semiconductor element was located in thexz-plane between θ=0° and θ=90°, a covering member thickness wasdifferent in that region. Because the covering member thickness was thesame in the other three quadrants, directional chromaticity graphs wereconsidered only for xz-plane measurements from θ=0° to θ=−90°. Further,because observation angles from θ=−80° to θ=−90° are essentiallyside-views of the light emitting device (in the x-axis or y-axisdirections of FIG. 5) and rarely viewed in practical applications,chromaticity evaluation was limited to the range from θ=0° to θ=−80°.Because large color differences occur at θ=−80°, directionalchromaticity results reported in Table 3 and Table 5 are colorcoordinate differences Δx, Δy for the color emitted at θ=−80°, withrespect to the color emitted at θ=0°.

TABLE 2 A wavelength A covering member Light conversion A Emittingmember Titanium Second covering Device First Oxide Second Fluorescentmember Size Fluorescent Content Fluorescent Material Content Thickness(mm × mm) Material (mass %) Material (mass %) (μm) Comparative 1.0 × 1.0SCASN-1, 60 — — 225 Example 1 SCASN-2  Comparative 0.8 × 0.8 SCASN-1, 60— — 300 Example 2 SCASN-2  First 1.0 × 1.0 SCASN-1, 60 SCASN-3 0.5 225Example SCASN-2  Second 1.0 × 1.0 SCASN-1, 60 SCASN-3 5.0 225 ExampleSCASN-2  Comparative 1.0 × 1.0 SCASN-1, 60 YAG 0.5 225 Example 3SCASN-2 

TABLE 3 Dominant Chromaticity Dominant Wavelength Luminous DirectionalChromaticity Coordinates Wavelength Difference Flux Ratio (xz-plane) x y(nm) (nm) (%) Δx(−80°) Δy(−80°) Comparative 0.654 0.338 609 — 100.0−0.006 −0.004 Example 1 Comparative 0.656 0.338 609 — 95.0 −0.001 −0.001Example 2 First 0.655 0.338 609 8 100.2 −0.003 −0.002 Example Second0.656 0.338 609 8 100.0 0.000 −0.001 Example Comparative 0.656 0.338 60934 100.7 −0.007 −0.003 Example 3

From Table 2 and Table 3, the light emitting device of comparativeexample 1 had color coordinate differences at θ=−80° (directionalchromaticity) of Δx=−0.006, Δy=−0.004 compared to the chromaticity atθ=0°. This means that the color emitted at θ=−80° was shifted towardsblue, which is the color emitted by the light emitting element. Further,actual visual observation of the illuminated light emitting deviceconfirmed a pink hue at θ=−80° different from the color emitted at θ=0°.

Because the light emitting element in comparative example 2 was smallerthan the light emitting element in comparative example 1, directionalchromaticity was better than that of comparative example 1. Actualvisual observation of the illuminated light emitting device could notconfirm any color difference at θ=−80°. Accordingly, if color coordinatedifferences Δx, Δy are within a range from −0.001 to +0.001, colornon-uniformity is essentially unobservable. However, because the lightemitting device of comparative example 2 had a smaller light emittingelement, the luminous flux ratio was reduced. Consequently, directionalchromaticity improvement without light emitting element size reductionwas not achieved.

By adding fluorescent material to the covering member of the lightemitting devices for the first and second examples, directionalchromaticity improvement was verified. SCASN-3 fluorescent material,which has a dominant wavelength 8 nm shorter than the dominantwavelength of the light emitting device, was used in the covering memberof the light emitting devices for the first and second examples, Inparticular, the second example, which incorporated 5.0 mass % offluorescent material in the covering member, had both directionalchromaticity coordinate differences Δx, Δy within the range from −0.001to +0.001 implying little color non-uniformity. Furthermore, theluminous flux ratio was effectively equivalent to that of comparativeexample 1.

Comparative example 3, which used YAG fluorescent material with adominant wavelength 34 nm shorter than the dominant wavelength of thelight emitting device, had a fluorescent material content of 0.5% in thecovering member, and results indicated that this approach could noteasily improve directional chromaticity differences.

The dominant wavelength of fluorescent material added to the coveringmember of the examples was less than or equal to 30 nm different fromthe dominant wavelength of the light emitting device. Comparing thesecond example, which had a fluorescent material content of 5.0 mass %,with the first example, which had a fluorescent material content of 0.5mass %, the absolute value of directional chromaticity coordinatedifferences Δx, Δy were smaller for the second example. Accordingly,fluorescent material content in the covering member is preferablygreater than 0.5 mass % with respect to the resin.

TABLE 4 A wavelength A covering member Light conversion A Emittingmember Titanium Second covering Device First Oxide Second Fluorescentmember Size Fluorescent Content Fluorescent Material Content Thickness(mm × mm) Material (mass %) Material (mass %) (μm) Comparative 1.0 × 1.0SCASN-1, 30 — — 225 Example 4 SCASN-2  Third 1.0 × 1.0 SCASN-1, 30SCASN-3 0.5 225 Example SCASN-2  Fourth 1.0 × 1.0 SCASN-1, 30 SCASN-35.0 225 Example SCASN-2 

TABLE 5 Chromaticity Dominant Dominant Luminous Directional ChromaticityCoordinates Wavelength Wavelength Flux Ratio (xz-plane) x y (nm)Difference (nm) (%) Δx(−80°) Δy(−80°) Comparative 0.654 0.336 609 — 98.3−0.020 −0.013 Example 4 Third 0.656 0.337 609 8 99.1 −0.009 −0.006Example Fourth 0.658 0.338 609 8 99.0 0.001 −0.001 Example

As shown in Table 4 and Table 5, comparative example 4, which included alower content of titanium oxide in the covering member compared tocomparative example 1, had degraded directional chromaticity.Specifically, comparative example 4 had directional chromaticitycoordinate differences of Δx=−0.020, Δy=−0.013 at θ=−80°. Compared tothe chromaticity at θ=0°, this represents a significant shift in thecolor emitted at θ=−80° towards the blue light emitted by the lightemitting element. Because the content of titanium oxide reflectingmaterial was reduced, the amount of light, particularly light emittingelement light, not reflected by titanium oxide and passing through thecovering member to the outside of the light emitting device was believedto have increased.

By addition of fluorescent material to the covering member of lightemitting devices for the third and fourth examples, directionalchromaticity improvement was observed. In particular, the fourth examplethat included 5.0 mass % of fluorescent material the same as the secondexample, which included 60 mass % titanium oxide, had both directionalchromaticity coordinate differences Δx, Δy within the −0.001 to +0.001range indicating practically no color non-uniformity.

The light emitting device of the present disclosure can be used inapplications such as automotive applications, indicator and displaydevices, illumination and lighting equipment, monitors and displays, andliquid crystal display backlight.

It should be apparent to those of ordinary skill in the art that, whilevarious examples of the invention have been shown and described, it iscontemplated that the invention is not limited to the particularexamples disclosed. Rather, the disclosed example should be consideredto be merely illustrative of the inventive concepts and should not beinterpreted as limiting the scope of the invention. The disclosedexamples may be modified and changed so long as they remain within thespirit and scope of the invention as defined in the appended claims.

What is claimed is:
 1. A light emitting device comprising: a lightemitting element having a dominant wavelength in a range greater than orequal to 380 nm and less than or equal to 470 nm; a wavelengthconversion member that is disposed on the light emitting element andcomprises: a translucent member, and a first fluorescent material layerinterposed between the light emitting element and the translucentmaterial, wherein the first fluorescent material layer comprises a resinthat contains a first fluorescent material, and wherein the firstfluorescent material comprises at least one compound selected from (Ca,Sr)AlSiN₃: Eu and (Ca, Sr, Ba)₂Si₅N₈: Eu; and a covering member thatcovers sides of the wavelength conversion member and surrounds the lightemitting element, wherein the covering member comprises light reflectingmaterial and a second fluorescent material, and wherein the secondfluorescent material comprises at least one compound selected from (Ca,Sr)AlSiN₃: Eu and (Ca, Sr, Ba)₂Si₅N₈: Eu; wherein the light emittingdevice has an emission spectrum having a dominant wavelength in a rangegreater than or equal to 610 nm and less than or equal to 780 nm; andwherein a dominant wavelength of an emission spectrum of the secondfluorescent material differs from the dominant wavelength of theemission spectrum of the light emitting device by less than or equal to30 nm.
 2. The light emitting device as cited in claim 1, furthercomprising: an adhesive layer interposed between the light emittingelement and the fluorescent material layer.
 3. The light emitting deviceas cited in claim 1, wherein the translucent member has a light emittingsurface coated with anti-reflection coating.
 4. The light emittingdevice as cited in claim 1 wherein an average particle diameter of thesecond fluorescent material of the covering member is less than or equalto 10 μm.
 5. The light emitting device as cited in claim 1 wherein anamount of the second fluorescent material of the covering member isgreater than or equal to 0.5 mass % and less than or equal to 10 mass %with respect to resin in the covering member.
 6. The light emittingdevice as cited in claim 1 wherein an amount of the light reflectingmaterial of the covering member is greater than or equal to 10 mass %and less than or equal to 100 mass % with respect to resin in thecovering member.
 7. The light emitting device as cited in claim 1wherein a minimum thickness of the covering member measuredperpendicular to a lateral surface of the light emitting element is lessthan or equal to 300 μm.
 8. The light emitting device as cited in claim1 wherein the light reflecting material of the covering member comprisesat least one compound selected from titanium dioxide, silicon dioxide,zirconium dioxide, and alumina.
 9. The light emitting device as cited inclaim 1 wherein a change in chromaticity coordinates with angulardirection from a direction perpendicular to a light emitting surface ofthe wavelength conversion member to a direction rotated by 80° is lessthan or equal to 0.003 in both x-axis and y-axis directions, where thex-axis and y-axis are mutually perpendicular and lie in the plane of thewavelength conversion member light emitting surface.
 10. The lightemitting device as cited in claim 1 wherein a chromaticity of lightemitted by the light emitting device is within a four-sided region on aCIE 1931 chromaticity diagram, where chromaticity coordinates (x, y) are(0.645, 0.335) at a first point, (0.665, 0.335) at a second point,(0.735, 0.265) at a third point, (0.721, 0.259) at a fourth point, and afirst line joins the first and second points, a second line joins thesecond and third points, a third line joins the third and fourth points,and a fourth line joins the fourth and first points to define thefour-sided region of the chromaticity diagram.